WASHINGTON - As the country awaits this month’s Supreme Court decision on the fate of President Obama’s sweeping health reform law, sharp negative questioning by justices during oral arguments has supporters and opponents girding for the possibility that the entire bill could be overturned.

That means the elimination - along with the controversial mandate that most people purchase health insurance - of popular provisions allowing young adults to stay on their parents’ insurance until age 26, making prescription drugs for seniors more affordable, and requiring insurers to cover those with pre-existing medical conditions without charging them more.

Even if the court were to strike just the individual mandate and keep the rest of the law intact, some health care advocates, insurers, and lawmakers fear that these consumer protections would be unable to stand on their own.

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“There are a series of provisions of the law which have already been enacted which have proven to be fairly popular,’’ said Andrew Dreyfus, president and CEO of Blue Cross Blue Shield of Massachusetts. “The question nationally is will there be bipartisan consensus to maintain those provisions even if the Supreme Court overturns some aspects of the law or the whole law?’’

Both Democrats and Republicans in Congress have been reluctant to openly discuss contingency plans, or the possibility of compromise, in the event the court strikes down the law. Both sides of the aisle agree that nothing will be accomplished prior to November’s presidential election.

Still, some House Republicans have quietly begun to discuss what elements of the law they would keep. The Republican mantra, after all, has been “repeal and replace’’ but not all party members are eager to craft a replacement. The issue remains divisive as Republicans face resistance from some of the more conservative members of their own party, who want full abolition of the law’s many provisions.

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“Repeal and replace is a good slogan, but what kind of replacement are we talking about?’’ said Gail Wilensky, a health economist who oversaw Medicare and Medicaid under George H.W. Bush. “Is it a replacement that will substantially extend coverage for people who have been uninsured? At the moment it’s a little hard to see that happening.’’

John McDonough, director of Harvard University’s Center for Public Health Leadership, criticized Republicans who oppose the law for moving to restore some of its popular consumer protections - like keeping young adults on their parents’ health insurance and other provisions that would primarily benefit middle- and upper-income people - instead of fighting for the law’s Medicaid expansion that would help more low-income people gain health insurance.

Although polling shows the nation remains sharply divided along partisan lines over health reform, a full-scale repeal could set off a backlash among the previously indifferent.

“It’s a standard rule of politics that people value losses more than hypothetical gains,’’ said McDonough, who helped the Senate craft the national health reform law. “If the court were to strike down significant parts of the law that are already in place, there could quite possibly be a potent public reaction against what is being taken away from people.’’

In addition to the popular consumer protections, the law requires insurers to offer preventative care for free and eliminates annual and lifetime limits on certain benefits.

Insurers and some Democratic lawmakers argue that it will become prohibitively expensive to keep the consumer protections without requiring most Americans to buy health insurance.

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James Roosevelt Jr., president and CEO of Tufts Health Plan, said that Tufts would probably continue to offer a plan that would do away with co-pays and deductibles for preventative care, and allow parents to keep their adult children on their health insurance, but it would cost members and employers extra.

“We can’t decide that all our plans are going to keep the things that were struck down that people liked in the Affordable Care Act, because our competitors would be out there saying, ‘If you want to pay less, come to us,’ ’’ Roosevelt said. “The benefit of the law is that you spread out the cost over everybody, which makes it more affordable for any individual person.’’

Some conservative policy makers disagree, saying the mandate could easily be separated from the rest of the law and there are alternatives that could preserve the consumer protections while making insurance more affordable.

Although Douglas Holtz-Eakin, who was Senator John McCain’s economic adviser during the 2008 presidential campaign, said he does not expect the court to scrap the entire law, he believes it best for Congress to start crafting a more incremental, far less sweeping bipartisan bill from scratch.

Instead of a mandate, the young and healthy could be motivated to buy health insurance if insurers must cover anyone with pre-existing medical conditions as long as the person remains continuously insured, he said.

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Other health experts do not foresee Washington easily replacing the Obama law.

“We would return to a world in which the well on health reform is poisoned in Congress,’’ said Drew Altman, chief executive of the Kaiser Family Foundation, a nonpartisan health policy group. “It’s become such an ideological hot potato, it’s hard to imagine Republicans and Democrats in a polarized Congress agreeing on health reform legislation for the foreseeable future, which would leave us at the mercy of the states doing what they can.’’

A total dismissal of the law would be detrimental to Massachusetts’ own efforts to expand insurance coverage, said Michael Miller, director of strategic policy at Community Catalyst, a Boston-based nonprofit that advocates for universal health care.

Although Massachusetts’ requirement that Bay State residents purchase insurance would not be threatened by a Supreme Court rejection of the Obama law’s mandate, the state is relying on a substantial expansion of Medicaid under national health reform - and the hundreds of millions in federal dollars that accompany it - to extend coverage to people, Miller said.

The state also stands to lose federal funding for community health centers, along with individual and small-employer tax credits, he said.

As the clock ticks towards decision time, the Legislature is doing what it can to preserve some of the national law’s more popular elements in case the law is struck down. Last month the state Senate amended its budget to include language that requires insurers to offer childhood immunizations without a copay or deductible. Some consumer advocate groups are also pushing the Legislature to add preventative services for free, as the national law requires.

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“The idea is to align ourselves as much as possible with the national law so in the case the entire thing gets wiped out, it would be on the books and would continue to be a part of Massachusetts state law,’’ said a Senate aide familiar with the legislation.